Min søster vil ikke købe hvad som helst til aftensmad.

Because in a normal Danish main clause, the finite verb usually comes in second position. Here, the finite verb is vil.

So the order is:

• Min søster = subject
• vil = finite verb
• ikke = negation
• købe = infinitive
• hvad som helst = object/expression meaning anything
• til aftensmad = for dinner

That gives:

Min søster vil ikke købe ...

This is very typical Danish word order. English often puts not right after the auxiliary too, so the pattern is not too strange:

• English: My sister will not buy ...
• Danish: Min søster vil ikke købe ...

It can suggest either, depending on context, but in this sentence it most naturally means something like is not willing to or won’t.

So Min søster vil ikke købe ... can feel like:

• My sister won’t buy ...
• My sister doesn’t want to buy ...

Danish vil often overlaps with English will/won’t, but it can also carry a sense of wanting or being willing.

Because it comes after the modal verb vil.

In Danish, after modal verbs such as:

• vil = will / wants to
• kan = can
• skal = must / shall
• må = may / must
• kunne = could
• ville = would

the next verb usually stays in the infinitive form.

So:

• vil købe = will buy / wants to buy
• not vil køber

That is similar to English:

• will buy
• not will buys

Hvad som helst means anything at all, just anything, or whatever.

In this sentence, it gives the idea that the sister is not willing to buy just any food for dinner. She is selective.

So the sentence does not simply mean she will buy nothing. It means she won’t buy just anything.

There is an important nuance:

• Hun vil ikke købe noget. = She won’t buy anything.
• Hun vil ikke købe hvad som helst. = She won’t buy just anything.

The second one implies she might buy something, but only if it meets some standard.

Yes, but the meaning shifts a little.

• ikke købe hvad som helst = not buy just anything / not buy whatever
• ikke købe noget som helst = not buy anything at all

So:

• Min søster vil ikke købe hvad som helst til aftensmad
  = She won’t buy just anything for dinner.

• Min søster vil ikke købe noget som helst til aftensmad
  = She won’t buy anything at all for dinner.

That difference is very useful. Hvad som helst suggests no random choice. Noget som helst often strengthens a complete negation.

Til aftensmad means for dinner.

The preposition til is commonly used in Danish when talking about food for a meal:

• til morgenmad = for breakfast
• til frokost = for lunch
• til aftensmad = for dinner

So this part tells you what the purchase is intended for.

A very literal way to think about it is for the purpose of dinner.

Because søster is a common gender noun in Danish, not a neuter noun.

Danish singular nouns usually belong to one of two genders:

• common gender → takes en, min
• neuter → takes et, mit

Since it is:

• en søster

you say:

• min søster

not:

• mit søster

In practice, it negates the verbal idea vil købe here.

So the meaning is not just buy not, but rather:

• is not willing to buy
• won’t buy

And because the object is hvad som helst, the full sense becomes:

• She won’t buy just anything for dinner.

So the negation affects the action together with the idea of unrestricted choice.

Yes, it is natural and idiomatic.

It sounds like something you would say if you mean your sister is picky, careful, or has standards about what she buys for dinner.

It suggests something like:

• she doesn’t buy random food,
• she wants something specific,
• she won’t settle for whatever is available.

In a yes/no question, the finite verb usually comes first:

• Vil min søster ikke købe hvad som helst til aftensmad?

That means:

• Won’t my sister buy just anything for dinner?

So compared with the statement:

• Min søster vil ikke købe hvad som helst til aftensmad.

the verb vil moves in front of the subject min søster.

Yes. Aftensmad is very common and means evening meal / dinner.

Another common word is:

• middag

But usage depends on region, family habits, and context. In many situations, aftensmad is the clearest and most neutral way to say dinner.

So in this sentence, til aftensmad is perfectly normal and clear.